Nonlinear microbial nutrient limitation responses to biodegradable vs. conventional microplastics under long-term...

The widespread application of plastic film mulch has led to the accumulation of microplastics (Mps) in agricultural systems, posing potential threats to soil health. However, the effects of biodegradable and conventional Mps on microbial nutrient limitation have not been extensively studied, particularly under long-term agricultural management practices. Here, we sampled a long-term agricultural management field platform (with various fertilization and cropping systems) and conducted a microcosm experiment involving two types of Mps. We used extracellular enzymatic stoichiometry and multiple regression models to assess microbial nutrient limitation and its associations with soil chemical and microbial properties. The results demonstrated that mineral fertilizer combined with straw most effectively alleviated microbial carbon (C) limitation, reaching a minimum value of approximately 0.61. Biodegradable and conventional Mps addition reduced microbial C limitation by 14.9 % and 12.6 %, respectively. Microbial phosphorus (P) limitation was affected by the three-way interaction among cropping systems, fertilization regime, and Mps addition. Notably, biodegradable Mps alleviated microbial P limitation more effectively than conventional Mps, particularly under mineral fertilization. A linear relationship between microbial C and P limitation was observed in the No-Mps condition, whereas Mps addition led to distinct nonlinear response patterns depending on Mps type. Regardless of Mps type, extracellular enzyme activities and microbial properties were identified as the key predictors of microbial nutrient limitation. Overall, this study highlights that optimized agricultural management-such as replacing conventional plastic films with biodegradable alternatives, especially when combined with straw return-can alleviate microbial nutrient limitation and contribute to maintaining the equilibrium of soil nutrient cycling.